1. Field of the Invention
The present invention relates to a material made of magnetic garnet single crystals formed by liquid-phase epitaxial growth (hereinafter, referred to as "LPE") and to a Faraday rotator using the same, and particularly to a material for a magneto-optical element having a composition of (RSmBi).sub.3 Fe.sub.5 O.sub.12 and to a Faraday rotator formed by superposing two kinds of LPE magnetic garnet films different in the wavelength dependence on the Faraday rotation coefficient.
2. Description of the Related Art
A material made of magnetic garnet single crystals, which has a Faraday effect, is used as an essential material for an optical isolator. At present, the optical communication uses the 1310 nm band and 1550 nm band. In recent years, as a material made of magnetic garnet single crystals used in these wavelength bands, a single crystal film (LPE film) formed on a non-magnetic garnet single crystal substrate by the LPE process has been mainly used. The reason for this is that the LPE process is excellent in terms of mass-production.
Incidentally, the wavelength multiplex transmission remarked as a future optical communication of a large capacity essentially requires a wide band optical isolator having a wide wavelength band in which the change ratio of a Faraday rotation coefficient to the wavelength is made small. For a 1550 nm band, there has been known a wide band optical isolator using a Faraday rotator formed of a Bi substituted Tb iron garnet (Takahiko Tamaki, "Development of a wide band optical isolator for wavelength multiplexing transmission": NHK Science and Technical Research Laboratories R&D, No. 20, August, 1992, pages 8-17).
However, any wide band optical isolator having a sufficient performance for a 1310 nm band has never been developed. For example, an LPE film having a composition of Tb.sub.1.85 Bi.sub.1.15 Fe.sub.4.75 Al.sub.0.25 O.sub.12 used for such a wavelength band is narrow in the wavelength band width, and it cannot be applicable for the wavelength multiplex communication. In view of the foregoing, even for a 1310 nm band, an optical isolator having a wide band comparable to that used for a 1550 nm band has been required to be developed.